Tim Cul­len’s forth­com­ing gov­ernor bid in Wis­con­sin will test the power of pro-uni­on rhet­or­ic in 2018. But his­tory com­plic­ates the Demo­crat’s mes­sage, even against Re­pub­lic­an Gov. Scott Walk­er, the poster child for lim­it­ing uni­ons’ power.

Cul­len, a long­time le­gis­lat­ive lead­er and state cab­in­et mem­ber, left the state Sen­ate in 2014 after gain­ing na­tion­al polit­ic­al fame three years earli­er when he and 13 oth­er le­gis­lat­ors fled to Illinois to pre­vent a vote on Re­pub­lic­ans’ con­tro­ver­sial pub­lic uni­on col­lect­ive bar­gain­ing re­forms.

But there are cracks in Cul­len’s pro­gress­ive bona fides that could hinder him in a primary. Walk­er, who is ex­pec­ted to seek a third term, has praised Cul­len for be­ing “pretty reas­on­able” for work­ing with the GOP be­fore and dur­ing the 2011 stan­doff, and Cul­len once told pro­test­ers they should be “more re­spect­ful” of Walk­er. In 2012, Cul­len even briefly left the Demo­crat­ic caucus while rep­res­ent­ing a Demo­crat­ic-lean­ing dis­trict.

Among po­ten­tial primary op­pon­ents, Rep. Ron Kind and state Sen. Kath­leen Vine­hout have ex­pressed in­terest in run­ning, and oth­er can­did­ates such as Dane County Ex­ec­ut­ive Joe Par­isi could join the fray.